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Description/Abstract

Granular materials, sourced from quarried natural aggregates, are usually specified as backfill to retaining walls. These natural materials are becoming a scarce and expensive resource, particularly in Southern England. If used for urban projects, they will inevitably lead to additional construction traffic, with associated environmental damage. At Wembley Stadium, the use of clay backfill, derived from the on-site excavations, provided significant environmental benefits and a sustainable solution. Approximately 130,000 cubic metres of clay backfill was placed behind different types of retaining wall, varying from large embedded bored pile walls up to ten metres high (both propped and anchored) to small L-shaped walls. In order to verify the acceptability of the use of clay backfill, which can lead to large swelling pressures developing on the back of retaining walls, novel investigation and analysis techniques were necessary. This included specialist laboratory testing, an earthworks trial, and non-linear numerical analyses (using the FLAC code). The use of clay backfill is compared to the use of granular backfill in the context of sustainability and a whole life cost approach to engineering solutions. Social, environmental and economic issues are considered in order to provide a quantitative assessment rather than a simple qualitative assessment of the sustainable nature of the resulting scheme, taking into account any alterations or additional work required to accommodate the use of the clay backfill